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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Is the CO2 effect saturated?

What the science says...

The notion that the CO2 effect is 'saturated' is based on a misunderstanding of how the greenhouse effect works.

Climate Myth...

CO2 effect is saturated
"Each unit of CO2 you put into the atmosphere has less and less of a warming impact. Once the atmosphere reaches a saturation point, additional input of CO2 will not really have any major impact. It's like putting insulation in your attic. They give a recommended amount and after that you can stack the insulation up to the roof and it's going to have no impact." (Marc Morano, as quoted by Steve Eliot)

The mistaken idea that the Greenhouse Effect is 'saturated', that adding more CO2 will have virtually no effect, is based on a simple misunderstanding of how the Greenhouse Effect works.

The myth goes something like this:

CO2 absorbs nearly all the Infrared (heat) radiation leaving the Earth's surface that it can absorb. True!

Therefore adding more CO2 won't absorb much more IR radiation at the surface. True!

Therefore adding more CO2 can't cause more warming. FALSE!!!

Here's why; it ignores the very simplest arithmetic.

If the air is only absorbing heat from the surface then the air should just keep getting hotter and hotter. By now the Earth should be a cinder from all that absorbed heat. But not too surprisingly, it isn't! What are we missing?

The air doesn't just absorb heat, it also loses it as well! The atmosphere isn't just absorbing IR Radiation (heat) from the surface. It is also radiating IR Radiation (heat) to Space. If these two heat flows are in balance, the atmosphere doesn't warm or cool - it stays the same.

Lets think about a simple analogy:

We have a water tank. A pump is adding water to the tank at, perhaps, 100 litres per minute. And an outlet pipe is letting water drain out of the tank at 100 litres per minute. What is happening to the water level in the tank? It is remaining steady because the flows into and out of the tank are the same. In our analogy the pump adding water is the absorption of heat by the atmosphere; the water flowing from the outlet pipe is the heat being radiated out to space. And the volume of water inside the tank is the amount of heat in the atmosphere.

What might we do to increase the water level in the tank?

We might increase the speed of the pump that is adding water to the tank. That would raise the water level. But if the pump is already running at nearly its top speed, I can't add water any faster. That would fit the 'It's Saturated' claim: the pump can't run much faster just as the atmosphere can't absorb the Sun's heat any faster

But what if we restricted the outlet, so that it was harder for water to get out of the tank? The same amount of water is flowing in but less is flowing out. So the water level in the tank will rise. We can change the water level in our tank without changing how much water is flowing in, by changing how much water is flowing out.

Similarly we can change how much heat there is in the atmosphere by restricting how much heat leaves the atmosphere rather than by increasing how much is being absorbed by the atmosphere.

This is how the Greenhouse Effect works. The Greenhouse gases such as carbon dioxide and water vapour absorb most of the heat radiation leaving the Earth's surface. Then their concentration determines how much heat escapes from the top of the atmosphere to space. It is the change in what happens at the top of the atmosphere that matters, not what happens down here near the surface.

So how does changing the concentration of a Greenhouse gas change how much heat escapes from the upper atmosphere? As we climb higher in the atmosphere the air gets thinner. There is less of all gases, including the greenhouse gases. Eventually the air becomes thin enough that any heat radiated by the air can escape all the way to Space. How much heat escapes to space from this altitude then depends on how cold the air is at that height. The colder the air, the less heat it radiates.

(OK, I'm Australian so this image appeals to me)

So if we add more greenhouse gases the air needs to be thinner before heat radiation is able to escape to space. So this can only happen higher in the atmosphere. Where it is colder. So the amount of heat escaping is reduced.

By adding greenhouse gases, we force the radiation to space to come from higher, colder air, reducing the flow of radiation to space. And there is still a lot of scope for more greenhouse gases to push 'the action' higher and higher, into colder and colder air, restricting the rate of radiation to space even further.

Further reading

Comments

Tom Curtis @#97 disputes that the heat transport from the surface into the atmosphere is almost a constant whatever the surface temperature.
He cites:
Increased wind due to increased temperature.
Changed Lapse Rate.
Change in surface emissivity.
Change in conductivity of the air due to higher moisture content.

These may all be true [I actually dispute Lapse Rate changes: the lapse rate is controlled by the total energy into the atmosphere - net radiation, condensation of water, conduction, which I claim is virtually constant. So the Lapse Rate is a constant and Lapse Rate feedback may be a furphy.] but the LHS of the equation is always the sunlight absorbed by the Surface. Unless the albedo or solar constant change, sunlight absorbed by the Surface is invariant.

On the RHS we have:
Surface Energy absorbed into the atmosphere (NET radiation, condensed water vapour, conduction) plus Surface Energy radiated direct to space through the window. This latter term is nearly a constant, particularly if CO2 is nearly saturated (which it seems to be. It might change by a few percent if CO2 doubles - I look forward to calculated values for a doubling of CO2).

If CO2 doubles we know that the LHS decreases by approximately 1W/m^2 (increased absorption of sunlight by CO2 in the upper atmosphere). This will approximately balance any decrease in Surface radiation through the window, so the Surface Energy absorbed by the atmosphere will remain the same.

In the headline post (advanced version) the author assumes a "final layer" which is a black body at 220DegK.

I have three objections to this:
1. The "Final Layer" is nothing of the sort. Photons are emitted at all levels. Absorption ensures that most never make it out to space through the fog of overlying gas. The average emission height is determined by absorption. In general this level will be different for every frequency.
2. The atmospheric gases are not black bodies - nothing like black bodies. Unlike solids or liquids they do not emit a continuous spectrum, but preferred frequencies (lines), the envelopes of which both in detail abnd as a conglomerate are far from a black body. See http://spectralcalc.com/spectral_browser/db_intensity.php. A black body curve is not appropriate and the "blackbody temperature" cannot be used to estimate the average height of emission.
3. It is implied that the amount of energy absorbed is the difference between two blackbody curves. This is an erroneous view.
Energy absorbed into the atmosphere is ALWAYS manifested as kinetic energy (atmospheric heat) at the point of absorption. That energy flows upward by convection and radiation, still manifested as kinetic energy. It is then radiated to Space by the GHGs, primarily Water Vapour, with a little from CO2 (15-18W/m^2) and Ozone. These GHG molecules are energised by collision with other air molecules (around 50 times per nanosecond) and if the energies are right and the star signs are right (ie around one chance in one hundred thousand) a photon is emitted at a preferred frequency. If that photon avoids absorption by other GHG molecules, it escapes to space and that energy is lost from the planet.

novandilcosid @100, in 97 I identified several factors on the RHS of the equation that result in changes in value on the LHS, specifically, in changes to the back radiation. I also identified factors which cause relative changes to the value of the terms on the RHS of the equation. As your argument requires that the LHS determine the value the values on the LHS, but not in turn have their values determined by factors on the RHS, your argument fails because the value of back radiation has been shown to be partially dependent on RHS factors. Further, your argument also depends on the two non-evaporative values on the RHS being constant, and this has also been shown to be false.

You chose to ignore that facts I have raised, and simply re-assert your position. Fine - that it your right, but it also make debate with you pointless and uninteresting. I will merely note that keeping your discussion factual seems a low priority to you.

Curiously, not only are you uninterested in trying to grapple with the facts I presented, you then go on to refute your own case. First, you indicate that rate of evaporation per degree C is not known, but according to you that value follows by straightforward reasoning from the energy balance equation. Further, you indicate that both constant RHS with a 2.5% increase in evaporation per degree C and a decreasing RHS with a 5% increase in evaporation per degree C are reasonable suppositions. However, both suggest decreases in the value of the non evaporative terms on the RHS, and the second suggests a much larger decrease. These are terms you require to be constant which changing temperature for your argument to succeed, but now you entertain the notion that they are anything but.

Tom Curtis wrote @103 above:
"in 97 I identified several factors on the RHS of the equation that result in changes in value on the LHS, specifically, in changes to the back radiation."

I think Tom is referring to a different equation to the one I have been using to establish that the Surface Energy absorbed by the atmosphere is nearly a constant, regardless of CO2 concentration or temperature. Naturally this would cause differences of opinion to arise!

I have ignored Tom's interesting observations simply because they are not relevant to the case - they amount to identifying variations in terms on the RHS of the equation, and these variations do not affect the hypothesis.

The LHS of this equation is only affected by the solar constant, atmospheric absorption of sunlight, and planetary albedo. [It does not contain Back_Radiation, that is within the first term of the RHS.]

The LHS is nearly constant. If CO2 is doubled we expect a REDUCTION of about 1W/m^2 due to increased atmospheric absorption of sunlight.

On the RHS, if CO2 is doubled, there will be a decrease of Surface Energy escaping to space through the window. How much is unknown by me (it is the subject of this thread, but there does not seem to be a number being cited) but I would expect it is of similar magnitude to the change in the LHS - a DECREASE of about 1W/m^2.

IF that is the case then the third term, Surface_Energy_Absorbed _into_the_Atmosphere is a constant. This term contains evaporation, conduction and net radiation, all of which are the varying quantities which Tom has identified. I make no comment on the veracity of his claims at this point, merely restating that this term must be nearly constant.

Tom writes: "You chose to ignore that facts I have raised, and simply re-assert your position."

I agree. I have ignored his points (this is not to say I don't find them interesting), as I believe them to be irrelevant to the point I have been making.

The Surface Energy absorbed by the atmosphere is nearly constant, regardless of surface temperature or atmospheric CO2 content.

Tom Curtis wrote @#103 above:
"Further, you indicate that both constant RHS with a 2.5% increase in evaporation per degree C and a decreasing RHS with a 5% increase in evaporation per degree C are reasonable suppositions. However, both suggest decreases in the value of the non evaporative terms on the RHS, and the second suggests a much larger decrease."

Tom is correct.
The terms within the term "Surface_Energy_Absorbed _into_the_Atmosphere" are Net_Radiation, Evaporation and Conduction.

It is known that evaporation INCREASES with temperature. All authorities agree on that. What is not known is by how much. Is it 2.5% (models), 5% (measurement), or 6.5% (Clausius-Clapeyron, assuming constant RH ) per DegC?

It is also known that Net_Radiation INCREASES with temperature. But it DECREASES with increased CO2 concentration (back radiation increases slightly as the average altitude from which CO2 earth-bound photons are emitted drops. This level is lower therefore warmer, so there is aqn increase in intensity.)

novandilcosid @104, I am dropping the debate about the relation between evaporative energy transfers and net radiation. It is too time consuming, and so far as I can tell almost irrelevant to this topic. Indeed the only relevance I can see to global warming is that if your theory were true, the Green House Effect would be stronger than it is currently predicted to be. That is because if the energy flow to the atmosphere were constant with temperature, the energy flow from the atmosphere to space must also be constant with constant insolation regardless of surface temperature. Therefore any adjustment to reduced outgoing radiation due to green house gases must be entirely compensated for by changes in surface temperature, rather than partly compensated for by increased atmospheric temperatures as currently believed.

So, unless you can provide a clear and succinct statement of your thesis and it relevance, I will consider it of topic and not worth the energy.

novandilcosid @99 asks, ""[H]ow much additional surface energy is absorbed outside the saturated 625-725 band, ie by how much does the window close, in W/m^2? The following chart from SOD shows the change in net forcing from a doubling of CO2:

The total forcing for such a doubling is, of course, 3.7 W/m^2, with the vast majority of that being in the wings. You will notice that this is the forcing at 200mb, ie the tropopause (as also for the graphs of transmitance and change in transmitance at @86 and 82 respectively.

novan will of course point to the influence of the stratosphere, but that is greatly exaggerated by him, and for two reasons. First, to a reasonable approximation the energy in the stratosphere comes from UV radiation absorbed by ozone. Increasing the CO2 concentration does not increase that energy. Rather, it cools the stratosphere by radiating away that energy more efficiently. The result is a slight increase of radiation in the primary band of CO2 emissivity, but a reduction in the IR radiation by ozone (the other main gas that radiates energy away from the stratosphere). The result in zero net change in the OLR.

The second effect relates to the exchange of IR energy between the top of the troposphere and the stratosphere. Increased CO2 concentration reduces IR radiation from the troposphere to the stratosphere, further cooling the stratosphere (although how strong this effect is a matter of debate). But the increased proportion of stratospheric energy radiated by CO2 means there is an increase in energy radiated from the stratosphere to the troposphere by CO2. This, however is again balanced by a reduction in the IR radiation emitted by ozone to the surface.

In Line by Line and energy balance models, these effects are taken into account in determining the forcing at the tropopause. Radiative forcing is, after all, "The radiative forcing of the surface-troposphere system due to the perturbation in or the introduction of an agent (say, a change in greenhouse gas concentrations) is the change in net (down minus up) irradiance (solar plus long-wave; in Wm-2) at the tropopause AFTER allowing for stratospheric temperatures to readjust to radiative equilibrium, but with surface and tropospheric temperatures and state held fixed at the unperturbed values."

Consequently the above graph of change in radiative forcing at 200 mb includes the effects of the changes in the stratosphere.

Of course, novan may well dispute this, so the best thing to do is to got to empirical data. Novan's thesis is that the net effect of adding CO2 to the atmosphere is to increase radiation to space from CO2, thus cooling the Earth. (See 81 and 89 above). The following are graphs of the change in IR radiation (measured as brightness temperatures) between 1970 and 1997. Figure b top shows the change in the tropical Pacific (between 10 degrees north and 10 degrees south); while figure b bottom shows the "near global" changes (between 60 north and 60 south). The middle shows the tropical case as predicted by a model.

The first think to notice is that in the CO2 emission wavelengths, the emissions are either reduced or barely increased in the tropical observations; and that for the "near global" observations and the simulation they are reduced. The second thing to notice is that the net radiation to space has increased in the tropical case (and possibly also, but slightly, in the "near global" case. This indicates an overall increase in temperature of the Earth/atmosphere system in 1997 relative to 1970 which is anomalously large compared to that expected by the GHE alone. The obvious reason for this is the 1997/1998 El Nino which commenced in April of 1997 (the data is for the April-June period).

The obvious thing to do is to remove the temperature effects from the record. Doing so reveals graph C in the figure (and figure 1 in the article above) which shows a clear reduction radiation in the CO2 band. Thus novan's thesis is clearly refuted by the observational data.

Tom Curtis responded at 107 to my very clear post at #104 in which I said:
"Solar_Radiation_Absorbed_into_the_Surface = Surface_Energy_Absorbed _into_the_Atmosphere + Surface _Energy_Radiated_through_the_Window_to_Space

The LHS of this equation is only affected by the solar constant, atmospheric absorption of sunlight, and planetary albedo. [It does not contain Back_Radiation, that is within the first term of the RHS.]

The LHS is nearly constant. If CO2 is doubled we expect a REDUCTION of about 1W/m^2 due to increased atmospheric absorption of sunlight.

On the RHS, if CO2 is doubled, there will be a decrease of Surface Energy escaping to space through the window. How much is unknown by me (it is the subject of this thread, but there does not seem to be a number being cited) but I would expect it is of similar magnitude to the change in the LHS - a DECREASE of about 1W/m^2.

IF that is the case then the third term, Surface_Energy_Absorbed _into_the_Atmosphere is a constant. This term contains evaporation, conduction and net radiation, all of which are the varying quantities which Tom has identified. I make no comment on the veracity of his claims at this point, merely restating that this term must be nearly constant."

Tom said: "unless you can provide a clear and succinct statement of your thesis and it relevance, I will consider it of topic and not worth the energy."

I am somewhat at a loss as to how to proceed. My post is very clear, and no error has as yet been demonstrated, Tom's previous efforts having been irrelevant to the discussion as they did not address the clear statements made.

For the record:
1. All the solar energy absorbed into the surface must be exported from the surface.
2. There are only two places that energy can go, either into the atmosphere or out into space.
3. The solar input is nearly constant (there is a small reduction if CO2 is increased) and we expect a small reduction in the export to space (the window slightly tightens).
4. That means that the export of energy from the surface into the atmosphere is nearly constant regardless of temperatures and CO2 concentrations

There are a couple of things to note:
5. The above assumes integration over the whole surface for one year then averaging. It also assumes a planet in equilibrium with Space.
6. A constant energy flow from the surface into the atmosphere means a constant lapse rate. The lapse rate does not change with more evaporation, because any increase in evaporation is offset by decreases in energy flows from net radiation/conduction.
7. It is untrue to say that increasing CO2 increases the amount of surface energy trapped by the atmosphere. That energy entrapment is essentially constant.

Response: (DB) Except that the energy balance at the TOA is not balanced; thefore the planet is not in equilibria in its energy budget. Your argument therefore fails this initial test.

Tom Curtis posted at #108:
"novandilcosid @99 asks, ""[H]ow much additional surface energy is absorbed outside the saturated 625-725 band, ie by how much does the window close, in W/m^2?" The following chart from SOD shows the change in net forcing from a doubling of CO2...

I note in passing that increased Radiative Forcing (=energy inbalance at the Tropopause) is entirely different to increased absorption of Surface Energy, so that Tom's entire post is a confusing non-response to the question.

Does anyone have a figure for the decrease in Surface Energy passing through the window due to a doubling of CO2 and assuming no temperature change at the surface?

Response: (DB) Your final assumption is flawed so your question is meaningless.

DB reponded to my post at #109 with "Except that the energy balance at the TOA is not balanced; thefore the planet is not in equilibria in its energy budget. Your argument therefore fails this initial test."

He is sort of correct: on short timescales and at particular locations, the planet is not in equilibrium with Space. The energy balance changes from positive to negative all the time. But INTEGRATED on long timescales that balance has to be stable. Otherwise the planet will change to make it so.

For example over the last 10 years the planetary average temperature has not changed. So the integration of energy input/output will be balanced or nearly so. That's what the Kiehl & Trenberth diagram used by the IPCC in 2007 says. (or are we saying that the IPCC was wrong to use that diagram?)

I fail to see therefore why my innocous observation that there is no change in surface energy into the atmosphere is invalidated.

Response:

[DB]

"But INTEGRATED on long timescales that balance has to be stable. Otherwise the planet will change to make it so."

On very long timescales, it is in balance. Right now, due to the forcing from CO2, it is not. So the planet is seeking to regain that balance by raising the tropospheric temperatures as well as sequestering heat/energy into the oceans. This is very basic, PRATT stuff.

"For example over the last 10 years the planetary average temperature has not changed."

Incorrect. This fails on multiple levels:

The global temperature record shows the most recent 10 year period as the hottest in the instrumental record.

Selecting a short 10 year period is cherry-picking, as that period is typically too short to carry statistical significance. However, allowing for exogenous factors, the planet has shown statistically significant warming since 2000.

I fail to see, therefore, why you cannot see your position is invalidated from the initial premise.

novandilcosid @110, your post to which I responded asked both about the change in transmittance (aborption of surface radiation), and the change in atmospheric emissions at the top of the atmosphere. This first was shown clearly in post 82. The combined effect was clearly shown in my first figure @108. You dismiss that because that highly relevant data was not in the exact format your required to impose your spin. You at the same time simply ignore the impirical data that refutes your thesis. Well, your game is now very clear, and it is not honest inquiry. If you ever want to try that, run a full Line By Line calculation of the emissions spectrum (as has been done by the people whose results you simply dismiss), and then if you come up with an interesting result, try again. In the mean time, I am not interested in pretending the partial calculation of a result on the back of an envelope can in any way refute the full calculation of the result with computers using a variety of methods, all coming up with essentially the same result.

In response to my question "Does anyone have a figure for the decrease in Surface Energy passing through the window due to a doubling of CO2 and assuming no temperature change at the surface?" DB wrote:
" Your final assumption is flawed so your question is meaningless"

The whole of this thread is about how much the window closes (note: not about the export to space but about the absorption of radiation). I'll ask the question a different way:
"What is the percentage change in the proportion of surface radiation absorbed by CO2 for a doubling of CO2?"

Response:

[DB] As the OP shows, the whole of this thread is about:

"If the CO2 effect was saturated, adding more CO2 should add no additional greenhouse effect. However, satellite and surface measurements observe an enhanced greenhouse effect at the wavelengths that CO2 absorb energy. This is empirical proof that the CO2 effect is not saturated."

novandilcosid, I note again that you are not really arguing that the CO2 greenhouse effect is saturated... you are arguing that it does not exist at all.

Yet you have refused to respond to the obvious questions that raises:

1: Why do Spencer, Christy, Pielke 1&2, and every other 'skeptic' scientist (not to mention all mainstream scientists and all physics texts on the subject) claim that CO2 DOES cause the planet to be significantly warmer than it would be without?

2: If CO2 and other atmospheric gases can only slightly decrease the amount of radiation reaching the surface and thus cause slight cooling as you claim, then why is the Earth more than 30 C warmer than could be explained by sunlight hitting an airless rock at this distance from the Sun?

You stand at odds with nearly two centuries of scientific understanding. How do you explain that?

You argue that energy in must equal energy out (though this isn't true when a system is not in balance), but ignore the fact that this says nothing about the actually relevant issue of energy within the system.

Consider a house (or planet Earth) which is receiving a fairly constant influx of energy from a furnace (or the Sun). Once equilibrium is reached the energy leaving must be equal to the energy entering... but the amount of energy within the system can be very different depending on how much insulation (or greenhouse gases) it has. One constant energy source... constant energy emission from the system... but DIFFERENT amounts of energy within the system and therefor different temperatures. Ergo all your arguments about energy in and energy out are irrelevant. The question at hand is energy within the system.

"I note in passing that increased Radiative Forcing (=energy inbalance at the Tropopause) is entirely different to increased absorption of Surface Energy, so that Tom's entire post is a confusing non-response to the question.

Does anyone have a figure for the decrease in Surface Energy passing through the window due to a doubling of CO2 and assuming no temperature change at the surface?"

The figure is 3.7 W/m^2. When CO2 is doubled, the window (i.e. transmittance) reduces by 3.7 W/m^2 and the atmosphere absorbs an additional 3.7 W/m^2 of surface emitted radiation, half of which goes down to the surface and half of which goes up out to space (1.85 W/m^2 up and down).

It has been claimed here and elsewhere that the halving effect is already accounted for in the 3.7 W/m^2 figure; however, I have not been able to verify this through numerous inquiries to the climate science community. No one can give me a straight answer, but I'm still working on it.

Response: (DB) In reality, you were given an answer, which you have chosen to ignore.

RW1 - Your erroneous "halving" has been addressed repeatedly, you have simply chosen to disregard the answers you have received. 3.7 W/m^2 is the drop in IR emitted to space for a doubling of CO2. This is due both to the rise in tropopause and effective emission altitude from increased CO2 concentration (and hence lower CO2 emitting temperature) and absorption band expansion.

The window decreases slightly, but the predominant change is decreased emissions across the CO2 absorption bands. Hence "If the net effect at the surface is 3.7 W/m^2, then the "window" should close by 7.4 W/m^2 when CO2 is doubled" is simply wrong. There are two effects, not one, and your insistence on assigning all change to one effect has been corrected over and over again.

Anyone interested in that discussion should look at the Lindzen and Choi thread, where RW1 and others were informed of the details over 448 postings. Please do not rehash that here. This thread is about CO2 saturation, and it is hence off-topic.

Re: my past post - CO2 effects are on topic. However, George White/co2isnotevil's incorrect assumptions about 'halving' really are not. 3.7 W/m^2 is the decrease in IR leaving the atmosphere for a CO2 doubling, as per line-by-line multi-level atmospheric modeling, CO2 spectra and physics, and confirmed by top of atmosphere satellite measurements.

"As has been said here, repeatedly, the 3.7 TOA number means that 7.4 W/m^2 is being absorbed and radiated isotropically from CO2."

There is definitely a halving effect. The fundamental question is if the 3.7 W/m^2 represents the post or pre halving effect. If it represents the post halving effect, as claimed here, then the "window" or transmittance (i.e. the amount of surface emitted that passes straight through the atmosphere unabsorbed and goes out to space) should reduce by 7.4 W/m^2.

RW1 - As has been said to you before, the windowing effect (where IR goes straight from the surface to space) is only part of the reduction in IR. The rest occurs in the full absorption bands (where IR from the surface makes it only 10's or 100's of meters before absorption), as increased CO2 concentrations raise the level of effective tropospheric radiation to colder altitudes.

Why are you disregarding that very significant effect? Why are you claiming that all of the IR decrease occurs by a reduction of the 40 W/m^2 window, when that is clearly not the case?

"As has been said to you before, the windowing effect (where IR goes straight from the surface to space) is only part of the reduction in IR. The rest occurs in the full absorption bands (where IR from the surface makes it only 10's or 100's of meters before absorption)"

When I refer to the "window", I mean transmittance - the amount of the whole spectrum of emitted surface power that passes through to space without being absorbed by the atmosphere (not just one particular band). This is the amount that should reduce by 7.4 W/m^2 if the referenced 3.7 W/m^2 is all incident on the surface as claimed when CO2 is doubled.

There appears to be some confusion in regards to the definition or use of the term "window". Some refer to this as the mostly transparent region between about 8u and 13u, but this is not how I use the term. Nor do I believe this is how 'novandilcosid' is using the term either.

You don't seem to understand that there are other parts of the spectrum besides the CO2 absorbing bands that are not completely saturated and a portion of surface emitted energy passes through them unabsorbed out to space. The aggregate amount that passes through the whole spectrum of emitted surface energy is the "window" or transmittance.

Trenberth et al 2009 has a transmittance or "window" of 70 W/m^2 (40 through the clear sky and 30 through the clouds). If when CO2 is doubled, the "window" decreases by 3.7 W/m^2 (or 7.4 W/m^2) and 1.85 goes up out to space and 1.85 goes down to the surface (or 3.7 goes up and 3.7 goes down) (*Trenberth actually has it being 52% up and 48% down).

RW1 - Got it, you are going to continue to disregard the spectra between 600-750 microns, let alone around 450 microns, where IR from the surface cannot reach space unintercepted, and where increasing CO2 concentrations raise the effective emission to space to higher/colder altitudes.

Quite frankly, I cannot take your discussion of the greenhouse effect seriously when you ignore major components like this.

I'm not disregarding any spectra. I'm also well aware there are bands that are saturated. I also agree that the CO2 absorbing bands are not saturated - there is room on the wings to expand and capture a little more outgoing surface power. This is where the additional 3.7 W/m^2 from 2xCO2 is coming from.

RW1 @127, I don't want to buy into another fruitless conversation but, Trenberth 09 shows a 40 Watt/m^2 atmospheric window, and also shows 30 W/m^2 emitted to space from cloud surfaces, with another 169 W/m^2 emitted from the atmosphere other than from clouds. These three combine to make up the OLR.

"RW1 @127, I don't want to buy into another fruitless conversation but, Trenberth 09 shows a 40 Watt/m^2 atmospheric window, and also shows 30 W/m^2 emitted to space from cloud surfaces, with another 169 W/m^2 emitted from the atmosphere other than from clouds. These three combine to make up the OLR."

I don't see how this is possible. Think about it. How can the clear sky atmosphere emit 169 W/m^2 to space when surface only emits about 131 W/m^2 to the clear sky in the first place? We know this because the ISCCP data says clouds cover 2/3rds of the surface, which means 1/3rd of the surface is clear sky. 396 W/m^2 x 0.33 = 131 W/m^2 emitted from the surface to the clear sky.

John Cook, Moderators - Might I suggest a thread on the Trenberth diagram and energy budget?

This has been repeatedly misunderstood, misquoted, and misused for more instances of mathturbation than just about any graphic I can think of.

- It's not a model, contains no information whatsoever about interdependent changes of climate elements upon perturbation.
- It's a four layer accounting of energy interchanges between these layers (Sun, surface, atmosphere, space). Some of these exchanges (161 insolation, the 40 W/m^2 "window" from surface to space) skip a layer, most do not.
- Energy entering a level of this accounting does not retain identity/sourcing with what goes out; it's all joules, all the way down, which for example is why the atmosphere can radiate 169 W/m^2.
- If somebody disagrees with a number in the Trenberth budget, they should take it up with Trenberth, who has done a clearly sourced and researched work with plenty of references to look at for each individual number. "I don't see how this is possible" is not a valid objection; it's certainly not science.

I might also add that Trenberth's "window" of 70 W/m^2 is not referenced in the paper. It appears to just be a rough estimate or guess. He also has greater than half of the surface power absorbed by the atmosphere being emitted up out to space, which is inaccurate. To get half up and half down requires a "window" of 82 W/m^2 with his numbers (396 - 82 = 314; 314/2 = 157; 239 + 157 = 396 at the surface).

Even this site's hfranzen from first the link I posted in #124 has diagram on page 19 of his paper showing a "window" of 88 W/m^2. Take a look:

Response: [muoncounter] We've been through the half up/half down bit before. By assuming that model, your argument is turning circular. You're also veering off topic (and it's hard to do both at the same time). This thread is on CO2 absorption band saturation.

Berényi - The infrared atmospheric window was derived in 1918 from the H2O spectra, first estimated (by hand) in 1928. Now the value of transmitted energy is determined as a side product of the line-by-line radiation models, to distinguish between surface radiation actually transmitting directly to space and atmospheric radiation on the edges of the window also radiating to space.

Trenberth may have thought that it wasn't necessary to to spend much time on a value that has been known for >80 years. A value you could have determined with a few moments of web search, I'll note.

which means 1/3rd of the surface is clear sky. 396 W/m^2 x 0.33 = 131 W/m^2 emitted from the surface to the clear sky.

I won't get into Trenberth's diagram with you again (entirely). I'll repeat that you don't understand it, you are making invalid assumptions, you don't understand enough of the underlying physics of atmospheric heat transfer, and this is all leading to gross misinterpretations.

However, concerning this particular statement of yours about "1/3rd ... clear sky"...

First, you can't just assume that because 1/3 of the sky is clear then that the clear sky absorbs 1/3 of the radiation. The ability to absorb long wave radiation is dramatically different between clear sky and clouds (clouds probably absorb substantially more, being made up of a powerful greenhouse gas, but I've never really seen any numbers on this).

Clouds and the radiative properties of the surface are also not evenly distributed over the globe, either in space or in time. Everything else is not homogeneous.

Second, you cannot ignore the non-radiative components (thermals and the release of latent heat).

Third, and most importantly, you cannot ignore a major element which is not included in the diagram, which is the transfer of heat between "clear sky" and clouds. What happens when a cloud dissipates? Does the heat vanish? Is it forced to instantly radiate up to space? Does it fall to the ground with the rain?

Hint: When a cloud absorbs LW radiation, it is capable of transferring that heat to the surrounding and pervading atmosphere (remember, a cloud isn't a solid object, it coexists in space with the O2/N2 of the atmosphere). So it doesn't really matter which absorbs the radiation. The atmosphere (consisting of "clear sky" and clouds) absorbs the radiation, and the two cannot be separated into distinct components re this diagram.

This diagram is not a GCM. It's just a diagram intended to help communicate the earth's energy budget to the casual viewer, and nothing more. You cannot read as much into it as you are attempting.

So, again:

1) You need to study more before you can comment on or interpret Trenberth's diagram.
2) Trenberth's diagram is not the topic of this thread.

[This will be my last post on the subject (here), so please don't come back with an angry list of "but what about this?" questions. I'm not biting.]

#136KR at 22:44 PM on 26 April, 2011Trenberth may have thought that it wasn't necessary to to spend much time on a value that has been known for >80 years. A value you could have determined with a few moments of web search, I'll note.

Really? I thought the proper way to determine values of physical quantities is to measure them. On the other hand Trenberth simply assumes it is 40 W/m2.

We can get a deeper insight into his thought process if we consider an old paper of his where the problem is elaborated on briefly.

"Some of the radiation leaving the atmosphere originates near the earth's surface and is transmitted relatively unimpeded through the atmosphere; this is the radiation from areas where is no cloud and that is present in the part of the spectrum known as the atmospheric window, taken here to be the wavelengths 8-12 µm (Fig. 7). The estimate of the amount leaving via the atmospheric window is somewhat ad hoc. In the clear sky case, the radiation in the window amounts to 99 W m-2 , while in the cloudy case the amount decreases to 80 W m-2, showing that there is considerable absorption and re-emission at wavelengths in the so-called window by clouds. The value assigned in Fig. 7 of 40 W m-2 is simply 38% of the clear sky case, corresponding to the observed cloudiness of about 62%. This emphasizes that very little radiation is actually transmitted directly to space as though the atmosphere were transparent".

Taken here to be & somewhat ad hoc, indeed. A value of 40 W/m2 would imply a broadband thermal infrared optical depth of 2.29 (which roughly means the average photon gets absorbed 2.29 times before it escapes to space).

On the other hand this value averaged over the entire surface is below 1.9, that is, total thermal radiation flux escaping from surface to space unimpeded is above 60 W/m2.

Trenberth's simple calculation makes two omissions. One is the polar window (above wavelength 16 μm), covered only by weak water vapor absorption lines, so in extremely dry regions (like polar ones) a considerable amount of radiation can get through in that frequency band. The other one is clouds. As clouds are always fractal structures, cloud covered surface has a fractal dimension less than 2 (and decreasing poleward). Cloud fraction is usually determined by counting cloudy vs. clear sky grid cells (pixels). However, the finer the grid resolution is, the less the ratio of cloudy pixels will be, because fractals are just like that. It means even in areas categorized as "cloudy" some thermal IR can get through to space unimpeded.

Therefore thermal IR radiation flux originating near the earth's surface and transmitted relatively unimpeded through the atmosphere is measured to be more than 40 W/m2, Trenberth's back-of-the-envelope calculation is only good as a lower bound.

An error on the order of ~20 W/m2 in one of the components is a serious one if an average planetary imbalance of less than 1 W/m2 is pursued.

There are a lot of uncertainties in the numbers Trenberth presents, as is clearly discussed in the article: amounts of convective activity, latent heat numbers from precipitation, large scale estimation of the surface radiance covering sufficient points to cover variation, etc. Others are much more certain: backradiation, insolation, and so on. Taken together, they add up to 10's of watts.

I should probably withdraw that assumption upon the realization that while clouds cover on average of 2/3 of the surface, they make up considerably less of the total volume of the troposphere (7%, Lelieveld et al., 1989; Pruppacher and Jaenicke, 1995).

This means the atmosphere has opportunities to absorb that same radiation before it reaches the clouds (in the lower, denser part of the atmosphere where there is substantially more CO2 and water vapor), as well as above the clouds.

Comparing the outgoing LW radiation by latitude and season versus the cloud distributions by latitude and season demonstrates an even greater imbalance that must be addressed.

Obviously, things are a lot more complex, and such a brash, broad assumption was unwarranted.

#139KR at 02:33 AM on 27 April, 2011Very good; looking up the references. Which, I'll note, support the value in the 2009 paper.

No, it does not. It supports only a claim the value in the 2009 paper should be at least 40 W/m2, but it can be larger by a wide margin. Trenberth fails to mention this detail.

Does that matter?

Yes, definitely. According to Trenberth there is a net heat transport of 23 W/m2 from surface to atmosphere by thermal IR radiation. On the other hand if global average window radiation is more than 60 W/m2, this heat transport is negligible and any net heat transport between surface and atmosphere is mediated by thermals and evaporation. That's a big difference.

It means the greenhouse effect is saturated indeed. Surface and atmosphere is in radiative equilibrium (as it should) except for the fraction of radiation that escapes directly to space.

For example if effective temperature of the surface is 289 K (16 °C), effective temperature of the atmosphere as seen from the surface is 277 K (4 °C) and window radiation is 62 W/m2, the above relation holds.

Value of net heat transport by radiation between surface and atmosphere has enormous physical consequences, so you can't miss it by 10's of watts and still claim the physics is understood.

I would suggest you obtain a modern copy of MODTRANS or other radiation modeling code and look at the results yourself. You should also (as Trenberth did) cross-examine satellite spectra, cloud coverage estimation on a global scale, and distribution of humidity over both ocean and land.

Once you've done so, and backed up your calculations, your numbers can be taken seriously. If operating from a summary that has been adjusted for internal consistency, with considerable uncertainty on some items - not even close. Please cf. my last link in this post.

There is also 17 W/m2, but that's for thermals, not "thermal IR radiation." It has nothing to do with radiated heat.

Beyond this, you say:

It means the greenhouse effect is saturated indeed.

I don't follow you. That is, I don't follow how the proportion of energy from thermals to that escaping through the atmospheric window can have anything to do with whether or not the greenhouse effect is saturated, one way or the other.

Honestly, I don't see how anyone could ever take any numbers from such a simple schematic and draw any conclusions whatsoever about the CO2 being saturated.

Listen, I have not said data were manufactured. It just came from nowhere in that paper, that's all. And this claim is true, you can verify it for yourself.

"That 40 W/m2 is not substantiated anywhere in the paper. It was just pulled into Fig. 1. out of thin air".

Later on I have found the source in a paper written by the same author 12 years earlier, but the 2009 paper lacked any pointer to the source, window radiation is not even mentioned in the text.

Also, the calculation in the 1997 paper is somewhat childish, to put it mildly. And presenting a lower bound as a best guess is misleading as well.

More importantly, as the lower atmosphere is heated from below (by absorbed short wave radiation at the surface), most of it is either unstable or marginally stable. If there is excess heat at the bottom, it simply overturns the air column, possibly producing some precipitation (and releasing latent heat) as well instead of proceeding upward painfully by repeated radiation emission/absorption events.

It is a well known fact thermal conductivity of gases is extremely low. When measuring this quantity, radiative and collisional heat transfer are not separated, so radiative heat transfer inside the atmosphere can't be substantial.

Environmental lapse rate is 0.0065 K m-1 while thermal conductivity of air is 0.024 W m-1 K-1 (that of CO2 is even lower, 0.015 W m-1 K-1). It means upward heat transfer without mass exchange is about 0.16 mW/m2, which is negligible.

If there is a ~23 W/m2 thermal flux in a substance along a 6.5×10-3 K m-1 temperature gradient (with no mass exchange), thermal conductivity is ~3.5 kW m-1 K-1, which is ridiculous. It is more than that of diamond (2.2 kW m-1 K-1), the best thermal conductor of all materials.

In rare cases when there is a strong thermal inversion, radiative heat transfer may be somewhat larger, but still rather small compared to other fluxes (and its sign is just the opposite).

If Trenberth's figures on surface radiation and back radiation are correct, physics tells us the global atmospheric window is some 50% larger than he claims.

#145 - BP
"It is a well known fact thermal conductivity of gases is extremely low."
That is something of a cherry-pick, since it ignores the well-known effects of gases in motion.

It is a well known fact that thermal conductivity of gases is extremely low, which is why gases make good thermal insulators if the possibility of convection is restricted, as in foams, wool fabrics, compressed straw, etc.

It is a well known fact that thermal transfer rate of gases is extremely high if the refresh rate of air flowing over a surface is high, which is why CPUs, air-cooled engines, radiators of water-cooled engines etc. work so well at transferring heat.

Fortunately, just like engineers, climate scientists know about convection and allow for it in their models.

Berényi - Also note that in sea level pressure, in the saturated CO2 bands, absorption distance is ~10 meters, not zero, and this distance increases with altitude and reduced CO2 concentration. For unsaturated wavelengths this absorption distance is much further.

Seriously, BP - you're obviously very intelligent. But a lot of very intelligent people have been working in this field for >100 years... if you think you have (once again - I recall about a dozen of these, in UHI, OHC, etc., that did not pan out) found an issue that all the bright people have missed, you might be correct. But it's far more likely that you've missed something.

"First, you can't just assume that because 1/3 of the sky is clear then that the clear sky absorbs 1/3 of the radiation."

I'm not claiming the clear sky absorbs 1/3rd of the radiation. I'm saying that 1/3rd of the average surface radiation is emitted to the clear sky. This amount represents the theoretical maximum that can be emitted to space from the clear sky atmosphere, which is less than 169 W/m^2 emitted by the atmosphere depicted by the Trenberth diagram.

"The ability to absorb long wave radiation is dramatically different between clear sky and clouds (clouds probably absorb substantially more, being made up of a powerful greenhouse gas, but I've never really seen any numbers on this)."

I'm well aware of this. I don't see how this contradicts anything I've said. Using Trenberth's numbers, the cloudy sky absorbs 89% of the LW surface radiation emitted to it. The clear sky only absorbs 69% of the surface radiation emitted to it.

"Clouds and the radiative properties of the surface are also not evenly distributed over the globe, either in space or in time. Everything else is not homogeneous."

I never claimed it was. Relative to the energy balance, the averages (cloudy vs. clear sky) are what matter.

"Second, you cannot ignore the non-radiative components (thermals and the release of latent heat)."

I haven't. I'm well aware of them.

"Third, and most importantly, you cannot ignore a major element which is not included in the diagram, which is the transfer of heat between "clear sky" and clouds. What happens when a cloud dissipates? Does the heat vanish? Is it forced to instantly radiate up to space? Does it fall to the ground with the rain?"

No heat vanishes. It's either is radiated out to space, radiated down to the surface or returned to the surface in kinetic form mainly via precipitation.

"Hint: When a cloud absorbs LW radiation, it is capable of transferring that heat to the surrounding and pervading atmosphere (remember, a cloud isn't a solid object, it coexists in space with the O2/N2 of the atmosphere). So it doesn't really matter which absorbs the radiation."

What's your point? That the clear sky absorbs LW too?

"The atmosphere (consisting of "clear sky" and clouds) absorbs the radiation, and the two cannot be separated into distinct components re this diagram."

The average clear vs. cloudiness comes from the ISCCP data - not the Trenberth diagram. If, as you claim, the diagram is not depicting a 40 W/m^2 "window" through the clear sky and a 30 W/m^2 "window" through the cloudy sky with a total of 169 emitted by whole atmosphere, show me the power in = power calculations that demonstrate it. I have done so.

"This diagram is not a GCM. It's just a diagram intended to help communicate the earth's energy budget to the casual viewer, and nothing more. You cannot read as much into it as you are attempting."

I never claimed the diagram is a GCM. It's an energy budget diagram. With the exception of the ISCCP data on clouds, everything it taken directly from the diagram.

This amount represents the theoretical maximum that can be emitted to space from the clear sky atmosphere, which is less than 169 W/m^2 emitted by the atmosphere depicted by the Trenberth diagram.

Wrong.

You are discounting energy from other sources (such as thermals, latent heat, energy absorbed directly from the sun, and energy transferred from clouds to the "clear sky," as you call it).

The input into the "clear sky" is 78 from the sun, 17 from thermals, 80 from latent heat, an unknown fraction of 396 from the surface, and an unknown amount transferred from clouds.

You cannot separate the clouds from the clear sky with that diagram. You can't figure out how much energy the "clear sky" has to emit. You can't do it, except in the single, explicit case in the diagram where outgoing LWR is separated between clouds and "clear sky."

You cannot back yourself into the numbers you'd like to see.

You can't do it.

You can't do it.

(And even if you could, it has no bearing whatsoever on the topic of the post, i.e. whether the CO2 effect is saturated.)